Topology collection method and dual control board device for a stacking system

ABSTRACT

The invention provides a topology collection method and dual control board device applicable to a stacking system comprising dual control board devices. A master control board of a dual control board device advertises through a stack port the topology information of the member device in which the master control board resides, including information about the master control board and, if a slave control board is present, information about the slave control board; and stores the topology information or updates the existing topology information upon receiving the topology information of the stacking system through the stack port, and backs up the stored topology information of the stacking system to the slave control board after the slave control board is inserted. This invention is applicable for collecting the topology information of a stacking system comprising distributed dual control board devices.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. §119(a)-(d) ofChinese Application 200910077232.6 filed on Jan. 20, 2009.

TECHNICAL FIELD

This invention relates in general to the field of network communicationsand, more particularly, to a topology collection method and dual controlboard device for a stacking system.

BACKGROUND OF THE INVENTION

Stacking technology enables two or more devices to be connected togetherto form a stacking system that can be managed as a single device, thusproviding high availability and scalability, and simplifying management.A stacking system can comprise centralized devices or distributeddevices. The devices of a stacking system are connected through stackcables in a daisy chain, ring, or star structure. Special topologymanagement software is used to collect the topology information and thechanges in the topology structure of the whole stacking system. Thepresent invention is primarily applicable for collecting topologyinformation in a daisy chain or ring structure.

Each member device of a stacking system comprising centralized devices,as shown in FIG. 1, has one or two stack ports, and periodicallybroadcasts topology advertisement messages through the stack port orports to inform other member devices in the stacking system of thetopology information of the sending member device. The topologyinformation sent by each member device includes the member device ID,priority information, whether the current member device is the masterdevice, bridge MAC addresses, and other topology information. One of themember devices in the stacking system is elected as the master deviceaccording to a predefined election strategy. The master device collectsthe topology information contained in the topology advertisementmessages sent by other member devices, generates the topologyinformation of the whole stacking system, and broadcasts the topologyinformation to other member devices. All the other member devices storethe topology information of the stacking system.

After storing the topology information of the stacking system, eachmember device maintains connections with neighboring devices by sendingout hello packets periodically. When a member device detects that aneighboring device fails, that is, the port is down, the member deviceinforms other member devices of the failure. The master device thenre-collects the topology information of each member device, andbroadcasts to other member devices the latest topology information ofthe stacking system, so that the member devices can update the storedtopology information of the stacking system in time. When a new memberdevice is introduced to the stacking system, the new member deviceinforms the whole stacking system of its existence. The master devicealso re-collects the topology information of each member device andbroadcasts the latest topology information of the whole stacking systemto other member devices, so that the member devices can update thestored topology information of the stacking system in time.

In a stacking system comprising distributed single control boarddevices, each member device comprises one control board, one or twostack boards, and multiple service boards, as shown in FIG. 2 a. Thestacking system collects the topology information in the same way as thestacking system comprising distributed devices. The topology informationadvertised by the distributed single control board devices includes theinternal topology information of the member devices, such as the slotnumbers.

In a stacking system comprising distributed dual control board devices,each member device has two control boards, as shown in FIG. 2 b. Thecontrol boards serve as the master control board and slave controlboard, respectively. Because both the master and slave control boardsrun topology management software, the two control boards serve as twotopology nodes in the stacking system. If the master control boardfails, the slave control board takes over the job of the master controlboard in time, and thus the stacking system can operate normally. Due toits particularity, a distributed dual control board device cannot usethe topology collection method for centralized devices and distributedsingle control board devices. A method suitable for collecting thetopology information of a stacking system comprising distributed dualcontrol board devices is needed.

SUMMARY OF THE INVENTION

The present invention provides a topology collection method and dualcontrol board device applicable to a stacking system comprising dualcontrol board devices.

A method for collecting the topology information of a stacking system,which is applicable to a stacking system comprising dual control boarddevices, comprises: employing a master control board of a dual controlboard device to advertise through a stack port the device topology,which includes information about the master control board and, if aslave control board is present, information about the slave controlboard; and the topology information of the stacking system or updatingthe existing topology information upon receipt of the topologyinformation, and backing up the stored topology information to the slavecontrol board if a slave control board is present.

A dual control board device, as a member device of a stacking system,comprises a master control board and a slave control board, wherein themaster control board advertises through a stack port the topologyinformation of the member device in which the master control boardresides, including information about the master control board and, if aslave control board is inserted into the device, information about theslave control board; stores the topology information or updates theexisting topology information upon receiving topology information of thestacking system through the stack port, and backs up the stored topologyinformation of the stacking system to the slave control board after aslave control board is inserted.

The slave control board stores the topology information of the stackingsystem or updates the existing topology information.

The preceding technical scheme shows that the master control board of adual control board device advertises topology information of the memberdevice in which the master control board resides. The topologyinformation includes information about the master control board and, ifa slave control board is present, information about the slave controlboard. Thus the master control board and the slave control board serveas two topology nodes in the stacking system topology. In addition,after storing or updating the topology information of the stackingsystem according to the received information, the master control boardbacks up the topology information to the slave control board, so thatthe slave control board can also establish the stacking system topology.Upon a master/slave switchover due to a master control board failure orremoval, the slave control board becomes the master control board intime, thus ensuring that the member device does not quit the stackingsystem and that services such as packet forwarding are performednormally according to the topology information of the stacking system.This invention is applicable for collecting the topology information ofa stacking system comprising distributed dual control board devices.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the structure of a stacking system comprisingcentralized devices.

FIG. 2 a illustrates the components of a single control board device.

FIG. 2 b illustrates the components of a dual control board device.

FIG. 3 is a flow chart of the method according to the embodiment of thepresent invention.

FIG. 4 illustrates the stacking system comprising dual control boarddevices according to the embodiment of the present invention.

FIG. 5 is a flow chart of master/slave switchover according to theembodiment of the present invention.

FIG. 6 illustrates the topology information of the stacking systemaccording to the embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

To clarify the aims, technical proposals, and advantages of the presentinvention, the present invention is described below in view of thedrawings and embodiments.

As shown in FIG. 3, the method provided by the present inventioncomprises the following steps.

At step 301, the master control board of a dual control board deviceadvertises through a stack port device topology information about themaster control board and, if a slave control board is present, about theslave control board.

At step 302, upon receiving topology information of the stacking systemthrough a stack port, the master control board stores the topologyinformation and, if the slave control board is present, backs up thetopology information to the slave control board.

The following describes the preceding method provided by the presentinvention. As shown in FIG. 4, in the stacking system comprises dualcontrol board devices, each dual control board device having separateslots, one for the master control board and the other for the slavecontrol board. That is, a member device may have two topology nodes thatcan be connected to other member devices through one or two stack ports.

The master control board of a dual control board device sends outtopology advertisement messages and hello packets. In addition toinformation about the master control board, the advertised topologyinformation of the dual control board device also includes informationabout the slave control board if a slave control board is present,because the latter actively sends its information to the master controlboard once inserted into the device. For example, if a dual controlboard device with member ID designated ID1 is installed with both themaster and slave control boards, the master control board advertises thetopology information including the member ID of this dual control boarddevice, priority information, internal topology connections, roles ofthe master and slave control boards, and bridge MAC addresses of themaster and slave control boards. If no master of the stacking system iselected, roles of the master and slave control boards are non-master bydefault. If the master control board is elected as the master of thestacking system, the role of the master control board is advertised asmaster in the topology information. Internal topology connections caninclude slot numbers and other information.

Returning to FIG. 3, at step 303, a system master board of the stackingsystem is elected from among the master control board of the dualcontrol board device and one or more control boards of the other memberdevices. The election strategy for the master device can be configuredas needed. For example, when the master control board of the memberdevice with the highest priority is elected as the master, and the slavecontrol board of that member device takes over the master role once themaster control board fails. Another example of the election strategy isthat the control board with the longest operation time or lowest MACaddress is elected as the master. Other examples are omitted here.

The master control board serving as the master collects the topologyinformation advertised by other master control boards to generate thetopology information of the whole stacking system, and then broadcaststhe topology information to other member devices in the stacking system.Upon receiving the topology information of the stacking system through astack port, a member device stores the topology information or updatesthe stored topology information, and backs up the stored topologyinformation to the slave control board if a slave control board ispresent. The backup operation can be performed according to a schedule,or when the topology information of the stacking system stored by themaster control board changes. The master control board backs up thetopology information of the stacking system to the slave control boardin time, so that the slave control board is also aware of the topologyinformation of the whole system. Once the master control board fails oris removed, the slave control board takes over the job of the mastercontrol board in time and ensures the normal operation of services suchas packet forwarding according to the stored topology information.

The following events may occur in a dual control board device:

Event 1: If a member device is not inserted with any slave controlboard, the master control board of the member device advertises thetopology information about the master control board only. When a slavecontrol board is inserted, the slave control board sends a registrationmessage periodically to the master control board after starting up. Themessage contains information about the slave control board and is sentout until an acknowledgement message is received from the master controlboard. Upon receiving the registration message, the master control boardobtains the slave control board information, sends an acknowledgement tothe slave control board, adds the information to the device topologyinformation to be advertised, and backs up the topology information ofthe stacking system stored to the slave control board. Due to the changein the device topology information advertised by the master controlboard, that is, the slave control board information is further included,the master device re-generates the topology information of the stackingsystem and broadcasts the information to other member devices for themto update.

Event 2: When the master control board fails or is removed, master/slaveswitchover occurs. That is, the slave control board becomes the mastercontrol board and takes over the job of the former master control board,including advertising the topology information of the member device inwhich the master control board resides, receiving the topologyinformation of the stacking system, and sending out hello packets tore-establish neighboring relations and the stacking topology. Thetopology information advertised includes information about the newmaster control board only.

If the faulty or removed master control board is the master, the newmaster control board takes over the master role, sets the role of themaster control board to master in the device topology informationadvertised, collects topology information of member devices, andgenerates and broadcasts topology information of the stacking system. Ifthe faulty or removed master control board is not the master, the roleof the master control board is not changed, and the new master controlboard takes over the job of the faulty master control board only.

As shown in FIG. 5, the flow chart of event 2 comprises the followingsteps.

At step 501, the master control board fails or is removed, and the localslave control board receives a switchover message.

The topology detection module in the slave control board detects thestatus of the master control board. The reception of a switchovermessage means that the master control board failed or was removed and amaster/slave switchover is required.

At step 502, the slave control board becomes the master control boardand takes over the job.

The new master control board starts to advertise the topologyinformation of the member device in which the master control boardresides, receives the topology information of the stacking system, andsends out hello packets to re-establish neighboring relations and thestacking topology. The topology information advertised includesinformation about the new master control board only.

At step 503, if the new master control board detects that the formermaster control board is the master, step 504 is executed; otherwise,step 506 is executed.

At step 504, the new master control board takes over the master role andbecomes the master.

At step 505, the new master control board informs other member devicesof the master/slave switchover and the new master role by broadcastingadvertisement messages, and takes over the master operations.

Other member devices update the topology information stored uponreceiving the advertisement messages sent by the new master controlboard.

At step 506, the new master control board informs other member devicesof the master/slave switchover by broadcasting advertisement messages.

At step 507, the master re-generates and broadcasts the topologyinformation of the stacking system upon receiving the master/slaveswitchover message.

Event 3: After detecting that the slave control board fails or isremoved, the master control board excludes the slave control boardinformation from the device topology information to be advertised andstops backing up the stored topology information of the stacking systemto the slave control board. When confirming that the topologyinformation of the master device or the topology information sent by themaster changes, the master re-generates and broadcasts the topologyinformation of the stacking system.

In addition, the stacking system's topology information generated by themaster can include the number of each board. Boards can be numberedaccording to the connection relations of each member device. The boardsinclude control boards, stack boards, and service boards. The numberingmethods can be as follows:

Method 1: The number of a board can comprise the member device ID andthe slot number. For example, on a member device whose device ID is 2,the master control board in slot 1 is numbered 2/1, the slave controlboard in slot 2 is numbered 2/2, stack board 1 in slot 3 is numbered2/3, and service board 1 in slot 5 is numbered 2/5.

Method 2: Each board is numbered according to the member device ID, slotnumber and the predefined numbering strategy. For example, suppose thenumbering strategy is set as follows: The number of a board in thestacking system=(member device ID−1)×maximum number of slots supportedby a member device+slot number. If the maximum number of slots a memberdevice supports in the stacking system is 12, the boards in slot 0, 1,and 5 of the member device whose member ID is 2 are numbered 12, 13, and17, respectively.

FIG. 6 shows the topology information of a stacking system. The topologyinformation includes the member device IDs, priorities, numbers ofboards in the stacking system, roles of master and slave control boards,and bridge MAC addresses of master and slave control boards.

The following describes the dual control board device provided in anembodiment of the present invention. The dual control board device cancomprise a master control board and a slave control board.

The master control board advertises through a stack port the topologyinformation of the member device in which the master control boardresides, including information about the master control board and, if aslave control board is inserted into the device, information about theslave control board; stores the topology information or updates theexisting topology information upon receiving the topology information ofthe stacking system through the stack port, and backs up the storedtopology information of the stacking system to the slave control boardafter a slave control board is inserted.

The slave control board stores the topology information of the stackingsystem or updates the existing topology information.

The topology information advertised by the member device with the mastercontrol board installed after the slave control board is insertedcomprises the member device ID, priority information, internal topologyinformation, role information about whether the master control board orthe slave control board is the master, and the bridge MAC addresses ofthe master and slave control boards.

In addition, before a master is elected in the stacking system, themaster control board also elects one of the master control boards as themaster according to the topology information advertised by memberdevices. After being elected as the master, a master control boardcollects the topology information advertised by other master controlboards, generates the topology information of the stacking system, andbroadcasts the topology information in the stacking system.

The detailed election strategy for the master can be as described in thepreceding methods.

According to the three events that may occur in a dual control boarddevice, the dual control board device also provides the following:

1. The slave control board, after being inserted into the dual controlboard device, can periodically send a registration message containingthe slave control board information to the master control board until itreceives an acknowledgement from the master control board.

The master control board, upon receiving a registration message, sendsan acknowledgement to the slave control board, adds the slave controlboard information to the topology information of the member device inwhich the master control board resides, and starts to back up the storedtopology information of the stacking system to the slave control board.

The master control board backs up the stored topology information of thestacking system to the slave control board as scheduled or when thetopology information of the stacking system changes.

2. The dual control board device, after detecting that the mastercontrol board fails or is removed, becomes the master control board,takes over operations of the master control board, and, if the formermaster control board is the master, takes over the master role andoperations.

3. After detecting that the slave control board fails or is removed, themaster control board excludes the slave control board information fromthe device topology information to be advertised and stops backing upthe stored topology information of the stacking system to the slavecontrol board.

According to the preceding events, the master control board serving asthe master also re-generates and broadcasts the topology information ofthe stacking system if a change is detected in the topology informationof the member device in which the master resides or in the topologyinformation received.

In the preceding structure, the master control board runs a topologymanagement protocol agent module and a topology management protocolmodule. The topology management protocol agent module exchanges messageswith and backs up the topology information of the stacking system to theslave control board. The topology management protocol module advertisesthe topology information of the member device, receives, stores andupdates the topology information of the stacking system, and transmitshello packets.

The preceding description shows that the master control board of a dualcontrol board device advertises topology information of the memberdevice in which the master control board resides, wherein the topologyinformation includes information about the master control board and, ifa slave control board is present, information about the slave controlboard. Thus the master control board and the slave control board serveas two topology nodes in the stacking system topology. In addition,after storing or updating the topology information of the stackingsystem according to the received information, the master control boardbacks up the topology information to the slave control board, so thatthe slave control board can also establish the stacking system topology.Upon a master/slave switchover due to a master control board failure orremoval, the slave control board becomes the master control board intime, thus ensuring that the member device does not quit the stackingsystem and that services such as packet forwarding are performednormally according to the topology information of the stacking system.

It is to be understood that the above description discloses preferableembodiments of the present invention, and is intended to be illustrativeand not restrictive. Various modifications, alternate constructions, andequivalents will be obvious to those with skill in the art. Thus, thescope of the present invention is limited solely by the metes and boundsof the appended claims.

1. In a first device communicatively coupled with each of one or moreother devices of a stacking system that includes the first device, amethod for managing topology information of the stacking system, themethod comprising: at a master control board of the first device,advertising first device topology information via a stack port on thefirst device, the first device topology information includinginformation about both the master control board of the first device anda slave control board of the first device; and receiving topologyinformation of the stacking system via the stack port, storing thereceived topology information of the stacking system on the mastercontrol board, and backing up the received topology information of thestacking system on the slave control board.
 2. The method of claim 1,wherein storing the received topology information of the stacking systemon the master control board comprises updating existing topologyinformation of the stacking system on the master control board.
 3. Themethod of claim 1, wherein backing up the received topology informationof the stacking system on the slave control board comprises backing up acopy of the received topology information of the stacking system fromthe master control board to the slave control board in response to atleast one of (i) a periodic backup operation of the master controlboard, and (ii) receiving topology information of the stacking systemthat differs from previously received topology information of thestacking system.
 4. The method of claim 1, wherein backing up thereceived topology information of the stacking system on the slavecontrol board comprises storing a copy of the topology information ofthe stacking system on the slave control board.
 5. The method of claim4, wherein storing a copy of the topology information of the stackingsystem on the slave control board comprises updating existing topologyinformation of the stacking system on the slave control board.
 6. Themethod of claim 1, further comprising: via the stack port, receivingrespective device topology information advertised from each of the oneor more other devices; and based both on the received, respective devicetopology information and on the first device topology information,electing a system master board of the stacking system from among themaster control board of first device and one or more control boards ofthe one or more other devices.
 7. The method of claim 6, whereinelecting a system master board of the stacking system from among themaster control board of first device and one or more control boards ofthe one or more other devices comprises electing the master controlboard of the first device as the system master board of the stackingsystem.
 8. The method of claim 6, further comprising: at the mastercontrol board of first device, collecting the respective device topologyinformation advertised from each of the one or more other devices; atthe master control board of first device, generating topologyinformation of the stacking system from the respective device topologyinformation and the first device topology information; and at the mastercontrol board of first device, broadcasting the generated topologyinformation of the stacking system to each of the one or more otherdevices.
 9. The method of claim 8, wherein the first device topologyinformation further includes a device ID of the first device, priorityinformation of the first device, internal topology information of thefirst device, a bridge MAC address of the master control board, a bridgeMAC address of the slave control board of the first device, and anindication of whether one of the master control board of the firstdevice and the slave control board of the first device is designated asthe system master board, and wherein, for each respective device of theone or more other devices, the respective device topology informationincludes: information about a master control board of the respectivedevice, information about whether a slave control board is present inthe respective device and if so, information about the slave controlboard of the respective device, a device ID of the respective device,priority information of the respective device, internal topologyinformation of the respective device, a bridge MAC address of the mastercontrol board of the respective device, if a slave control board ispresent in the respective device, a bridge MAC address of the slavecontrol board of the respective device, and an indication of whether oneof the master control board of the respective device and the slavecontrol board of the respective device is designated as the systemmaster board.
 10. The method of claim 9, wherein the internal topologyinformation of the first device comprises a slot number for each of oneor more device boards installed in the first device, including themaster control board of the first device, wherein, for each respectivedevice of the one or more other devices, the internal topologyinformation of the respective device comprises a slot number for each ofone or more device boards installed in the respective device, whereinthe topology information of the stacking system comprises a uniqueidentifier for each respective device board of a plurality of deviceboards of the stacking system, the plurality of device boards includingthe one or more device boards installed in the first device and the oneor more device boards installed in each respective device of the one ormore other devices, and wherein the unique identifier of each respectivedevice board associates the respective device board with the device inwhich the respective board is installed.
 11. The method of claim 1,further comprising: at the slave control board, taking over operationsof the master control board in response to an occurrence of a failurecondition, the failure condition being at least one of failure of themaster control board, and removal of the master control board from thefirst device.
 12. The method of claim 11, wherein the master controlboard is a system master board of the stacking system when the failurecondition occurs, and wherein taking over operations of the mastercontrol board comprises taking over operations of the system masterboard of the stacking system.
 13. The method of claim 1, furthercomprising: in response to an occurrence of a failure condition, thefailure condition being at least one of failure of the slave controlboard, and removal of the slave control board from the first device:excluding information about the slave control board of the first devicefrom the advertised first device topology information, and ceasingbacking up the received topology information of the stacking system onthe slave control board.
 14. The method of claim 1, further comprising:electing the master control board of the first device as a system masterboard of the stacking system; at the system master board of the stackingsystem collecting respective device topology information advertised fromeach of the one or more other devices, generating topology informationof the stacking system from the respective device topology informationand the first device topology information, and broadcasting thegenerated topology information of the stacking system to each of the oneor more other devices; and thereafter regenerating and rebroadcastingthe topology information of the stacking system at the system masterboard of the stacking system in response to detecting a topology changecondition, the topology change condition being at least one of a changein the first device topology information, and a change in the respectivedevice topology advertised from at least one of the one or more otherdevices.
 15. In a first device communicatively coupled with each of oneor more other devices of a stacking system that includes the firstdevice, a method for managing topology information of the stackingsystem, the method comprising: at a master control board of the firstdevice, advertising first device topology information via a stack porton the first device, the first device topology information includinginformation about the master control board of the first device; via thestack port, receiving topology information of the stacking system,storing the received topology information of the stacking system on themaster control board; upon insertion of a slave control board into thefirst device, periodically sending a registration message from the slavecontrol board to the master control board of the first device until theslave control board receives an acknowledgement from the master controlboard of the first device, the registration message containinginformation about the slave control board; and upon receiving theregistration message at the master control board of the first device:sending an acknowledgement to the slave control board, adding the slavecontrol board to the advertised first device topology information, andbacking up the received topology information of the stacking system onthe slave control board.
 16. A first device to operate in a stackingsystem that includes one or more other devices, the first devicecomprising: a stack port for communication with each of the one or moreother devices of the stacking system; a master control board; and aslave control board, wherein the master control board is to: advertisefirst device topology information via the stack port, wherein the firstdevice topology information includes information about both the mastercontrol board and the slave control board, receive topology informationof the stacking system via the stack port, store the received topologyinformation on the master control board, and back up the receivedtopology information of the stacking system on the slave control board.17. The first device of claim 16, wherein the master control board is tostore the received topology information by updating existing topologyinformation of the stacking system previously stored on the mastercontrol board.
 18. The first device of claim 16, wherein the slavecontrol board is to store the topology information of the stackingsystem backed up from the master control board.
 19. The first device ofclaim 18, wherein the master control board is to back up the receivedtopology information of the stacking system on the slave control boardby backing up a copy of the received topology information of thestacking system from the master control board to the slave control boardin response to at least one of (i) a periodic backup operation of themaster control board, and (ii) receiving topology information of thestacking system that differs from previously received topologyinformation of the stacking system.
 20. The first device of claim 18,wherein the slave control board is to store the topology information ofthe stacking system by storing a copy of the topology information of thestacking system on the slave control board.
 21. The first device ofclaim 20, wherein storing a copy of the topology information of thestacking system on the slave control board comprises updating existingtopology information of the stacking system previously stored on theslave control board.
 22. The first device of claim 18, wherein themaster control board is further to: receive via the stack portrespective device topology information advertised from each of the oneor more other devices; based both on the received, respective devicetopology information and on the first device topology information, electa system master board of the stacking system from among the mastercontrol board of first device and one or more control boards of the oneor more other devices; and operate as the system master board of thestacking system upon being elected to do so.
 23. The first device ofclaim 22, wherein the master control board is to operate as the systemmaster board by: receiving via the stack port respective device topologyinformation advertised from each of the one or more other devices;collecting the respective device topology information advertised fromeach of the one or more other devices; generating topology informationof the stacking system from the respective device topology informationand the first device topology information; and broadcasting thegenerated topology information of the stacking system to each of the oneor more other devices.
 24. The first device of claim 18, wherein theslave control board is further to take over operations of the mastercontrol board in response to an occurrence of a failure condition, thefailure condition being at least one of failure of the master controlboard, and removal of the master control board from the first device.25. The first device of claim 24, wherein the master control board isfurther to operate as a system master board of the stacking system, andthe slave control board is further to take over operations of the mastercontrol board at least by taking over operations of the system masterboard of the stacking system.
 26. The first device of claim 18, whereinthe master control board is further to: in response to an occurrence ofa failure condition, the failure condition being at least one of failureof the slave control board, and removal of the slave control board fromthe first device: exclude information about the slave control board ofthe first device from the advertised first device topology information,and cease backing up the received topology information of the stackingsystem on the slave control board.
 27. The first device of claim 23,wherein the master control board is further to operate as the systemmaster board by: regenerating and rebroadcasting the topologyinformation of the stacking system at the system master board of thestacking system in response to detecting a topology change condition,the topology change condition being at least one of a change in thefirst device topology information, and a change in the respective devicetopology advertised from at least one of the one or more other devices.28. The first device of claim 16, wherein the master control board isfurther to: receive a registration message from a slave control board ofthe first device; and responsively, send an acknowledgement to the slavecontrol board, add the slave control board to the advertised firstdevice topology information, and back up the received topologyinformation of the stacking system on the slave control board.
 29. Thefirst device of claim 18, wherein the slave control board is further toinitialize its operation upon being inserted into the first device byperiodically sending a registration message to the master control boarduntil the slave control board receives an acknowledgement from themaster control board, wherein the registration message containsinformation about the slave control board.